btrfs: replace: drop assert for suspended replace

If the filesystem mounts with the replace-operation in a suspended state
and try to cancel the suspended replace-operation, we hit the assert. The
assert came from the commit fe97e2e1 ("btrfs: dev-replace: replace's
scrub must not be running in suspended state") that was actually not
required. So just remove it.

 $ mount /dev/sda5 /btrfs

    BTRFS info (device sda5): cannot continue dev_replace, tgtdev is missing
    BTRFS info (device sda5): you may cancel the operation after 'mount -o degraded'

 $ mount -o degraded /dev/sda5 /btrfs <-- success.

 $ btrfs replace cancel /btrfs

    kernel: assertion failed: ret != -ENOTCONN, in fs/btrfs/dev-replace.c:1131
    kernel: ------------[ cut here ]------------
    kernel: kernel BUG at fs/btrfs/ctree.h:3750!

After the patch:

 $ btrfs replace cancel /btrfs

    BTRFS info (device sda5): suspended dev_replace from /dev/sda5 (devid 1) to <missing disk> canceled

Fixes: fe97e2e1 ("btrfs: dev-replace: replace's scrub must not be running in suspended state")
CC: stable@vger.kernel.org # 5.0+
Signed-off-by: Anand Jain <anand.jain@oracle.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/dev-replace.c

@@ -1129,8 +1129,7 @@ int btrfs_dev_replace_cancel(struct btrfs_fs_info *fs_info)
 		up_write(&dev_replace->rwsem);
 
 		/* Scrub for replace must not be running in suspended state */
-		ret = btrfs_scrub_cancel(fs_info);
-		ASSERT(ret != -ENOTCONN);
+		btrfs_scrub_cancel(fs_info);
 
 		trans = btrfs_start_transaction(root, 0);
 		if (IS_ERR(trans)) {